Point contact densification

Abstract

A method of densifying a sintered powder metal article by point contact.

Description

This invention relates to a method of densifying a sintered powder metal article by point contact and in particular relates to a point contact densification of a sintered powder metal article by pressing and traversing said point across said powder metal article to define a densified surface.BACKGROUND TO THE INVENTIONVarious strides have heretofore made in order to produce high quality sintered powder metal articles whether in the form of gears, backing plates or the like.Various processes and apparatus have been devised in the prior art so as to increase the density of sintered powder metal article. For example, U.S. Pat. No. 3,795,129 relates to a method of forging a sintered article having a high density which method comprises pre-heating the forging tool of a forging machine and heating a preshaped powdering article and forging said heated preshaped powder article by said pre-heated tool.U.S. Pat. No. 3,874,049 teaches a method of forming powder metal parts having a bearing sur...

AI Technical Summary

Benefits of technology

Described Herein Include:1. High contact pressures with small applied force means more uniform densification of PM structures.2. The forces required are brought within range of normal CNC lathe turret forces.3. Genereally speaking any geometry that can be produced by CNC means can be densified in this way.4. The process is more controllable because the surface can be machined for precise location, immediately prior to densification.5. Fewer stress reversals means less "damage" to the structure.6. Some applications have indicated that the degree of sliding in the tool action is important to the level of densification. This can be controlled by presenting the tool with a pitch or alignment error such as shown by tool 4a in FIG. 12 (i.e. the tool is not normal or perpendicular to the axis of the workpiece or face as shown in FIG. 3).7. The force required to roll a surface can change as the traverse proceeds. This indicates that wrong action is taking place and that the leading radius should be modified. The leading and trailing rolling forces can be balanced by varying the radii at these locations.8. There is no dwell required as with the case 4 rolling by line contact. For example, if we look at FIG. 2, two rollers we used so that there is a dwell of 180.degree.. By densifying by point contact there is no dwell, and therefore the rates of rolling are much higher than with line contact.9. The rolling tools are reusable after regrind of the form.10. The process can be carried out dry because of the fewer number of working parts.11. The localized closure of porosity can reduce / anticipate heat treatment distortion.12. By varying the number of rolls and also the progression of radii r at the tips, greater depths of densification can be obtained than that shown in the prior art. This is illustrated in FIG. 16.For example, two or more tools 4.sub.L and 4.sub.S used are shown in FIG. 16. Generally speaking the larger the radius r.sub.L of a tool 4.sub.L used the greater the depth of densification for the same depth of penetration or closure. However it has been found that if a second tool 4.sub.S is used to densify by point contact after using a tool 4.sub.L t to densify by point contact the effect or depth densification is greater than if only one tool 4.sub.S was used. It is speculated that the reason for this is that once the surface has been densified by tool 4.sub.L the "pores" in the PM part have been collapsed and therefore the effect of densification of tool 4.sub.S is deeper than if only one tool 4.sub.S was used for the same closure.

Problems solved by technology

Generally speaking since such prior art sintered powder metal article are densified along "line" of contact high densifying forces are required which therefore result in lower tool life.

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